750kg
B&B is spot on that 750kg can and does make all the difference.
I tend not to think of fuel in Kg, as such. To me it is time aloft.
You want to hold for an hour. You need 2.5t ish for a 737.
There are lots of methods used to reduce the fuel load required for the trip, as B&B has mentioned. Winglets are but one of them.